- Tricia Miller, The Pennsylvania State University and Carnegie Museum of Natural History
- Todd Katzner, National Aviary
- David Brandes, Lafayette College
- Michael Lanzone, Carnegie Museum of Natural History
- Dan Ombalski, State College Bird Club
The size of the eastern North American population of golden eagles is small and therefore highly vulnerable to demographic perturbations. Even low levels of turbine-associated or other mortality may be significant for long-lived species with low reproductive rates and slow maturation rates (Drewitt and Langston, 2006; Katzner et al. 2006). Golden eagles tend to migrate and winter within areas of the central Appalachians that are currently under development or targeted for future development by wind energy companies. This species commonly uses slope soaring and ridge updrafts during migration and foraging, flight patterns which are known to increase collision risk (Barrios & Rodriguez, 2004; Hoover & Morrison, 2005). Additionally, a pilot study conducted by Farmer (2007) found that 88% of migrating bald and golden eagles flew at an altitude within the rotor swept area of modern turbines. It is for these reasons and others that golden eagles therefore may be highly susceptible to collision with some wind turbines (Hunt, 2002; Smallwood & Thelander, 2004). Because of their demography, migration and winter flight behavior, and vulnerability to wind turbines, we consider eastern golden eagles to be the raptor species at greatest risk of population-wide impacts from wind energy development in the Appalachians.
Available monitoring data and modeling strongly suggest that eastern golden eagles migrate through a narrow corridor in south-central Pennsylvania (particularly during spring; Brandes & Ombalski, 2004). This corridor includes portions of Bedford, Blair, Centre, Fulton, Huntingdon, Mifflin, and Somerset Counties and likely extends southward through Maryland into West Virginia. Thus, we consider the Allegheny Front and the five adjacent ridges to the east to be a zone of high risk for potential impacts to golden eagles.
Our tracking data show that three of five golden eagles that migrated through Pennsylvania used the area in and around Ice Mountain. Data points were collected at one-hour intervals. One bird roosted within the proposed facility and the data suggest that this bird foraged in the same area. There were a total of 19 hourly locations within 3000 m of the facility, with eight points falling within 300 m of a turbine. The closest location to a proposed turbine location was 65 m. Of the 19 points, 17 locations were stationary, while two locations were from two different birds in active flight. The altitudes of these two points were 1086 m and 849 m above sea level. The mean total height (elevation plus turbine height) of the turbines at Ice Mountain is 855 m ± 35 m. Thus, one of the flight locations was within the rotor swept area of the turbines at Ice Mountain. Based on these preliminary data, Ice Mountain appears to provide important migratory habitat for golden eagles.
In addition to the high use wintering areas on West Virginia and parts of Virginia, our preliminary telemetry data and remote camera surveys suggest that many more golden eagles winter in Pennsylvania than was previously known. Importantly, for the two telemetered birds that wintered in Pennsylvania, greater than 95% of their telemetry points were located in high elevation, remote wooded areas. This suggests that, in addition to providing important migration habitat, Ice Mountain may provide prime golden eagle wintering habitat. Furthermore, studies suggest that raptors are at highest collision risk when foraging (Hunt, 2002; Hoover & Morrison, 2005), thus land managers should consider the potential conflicts that wind energy facilities may pose, not only in critical migratory habitat, but in important wintering areas as well.
To summarize, our data tell us that golden eagles will be impacted by wind power development on Ice Mountain. Nevertheless, they do not tell us the scale of that impact - how many golden eagles may be at risk from wind power development at Ice Mountain, nor do they tell us exactly what will happen to eagles, should turbines be built there. The decision to put turbines at this site will have consequences for these Pennsylvania ridge tops and there will be impacts on golden eagles and other species. We hope that our limited preliminary data are useful to those of you who will make the decision whether or not to develop this site.